The NIH Exploratory Trials in Parkinson's Disease (NET-PD) program was established to facilitate the development of therapies to slow the progression of this chronic neurodegenerative disease. This network effectively executed futility studies of candidate therapies, which identified creatine as a having therapeutic potential. A subsequent Phase 3 efficacy trial, known as Long-term Study 1 (LS1) was designed and is being executed to evaluate the efficacy of creatine in slowing clinical decline in Parkinson's Disease (PD). LS1 is currently operational and has successfully met recruitment goals. Participants are being followed for a minimum of 5 years and maximum of 8 years. As a result, the final study visits will occur between June 2014 and May 2015. The current application requests funds to carry out Clinical Coordination Center activities through the completion of the NET-PD trials. These activities are guided by the following specific aims. Specific Aim 1 is to complete follow-up and enhance retention of enrolled participants in LS1 in order to test the primary hypothesis that daily administration of creatine (10gm/day) is more effective than placebo in slowing clinical decline in PD against the background of dopaminergic therapy and best PD care. Specific Aim 2 is to perform secondary analyses to evaluate the efficacy of creatine on individual PD clinical measures between baseline and the final follow-up visit that encompasses 5-8 years of study participation, as well as analyses of overall safety and tolerability. Specific Aim 3 is to continue to operate a Clinical Coordination Center for the completion of NET-PD studies, which involves (a) maintenance of study protocols, (b) Clinical Site oversight and training, (c) maintenance of quality and regulatory standards, (d) logistical oversight of experimental treatment distribution to Clinical Sites, (e) receipt and management of all clinical trial data, (f) close out the database and transfer to the Statistical Coordination Ceter for analysis, (g) participation in the analysis plans, interpretation and reporting of the trial reults, and (h) assisting the Statistical Coordinating Center in documenting and archiving the data in a publicly available database. Specific Aim 4 is to maintain an administrative structure that allows close collaboration with the Statistical Coordination Center, the Clinical Sites, NINDS Scientific Program personnel, the NINDS Data and Safety Monitoring Board and the NINDS Oversight Committee. Successful completion of these aims will achieve the goal of the NET-PD program to establish an innovative, evidence-based process by which potential therapies are selected and tested for slowing of PD progression.